A changing role for transitional probabilities in word learning during the transition to toddlerhood?

Infants' sensitivity to transitional probabilities (TPs) supports language development by facilitating mapping high-TP (HTP) words to meaning, at least up to 18 months of age. Here we tested whether this HTP advantage holds as lexical development progresses, and infants become better at forming word-referent mappings. Two groups of 24-month-olds (N = 64 and all White, tested in the United States) first listened to Italian sentences containing HTP and low-TP (LTP) words. We then used HTP and LTP words, and sequences that violated these statistics, in a mapping task. Infants learned HTP and LTP words equally well. They also learned LTP violations as well as LTP words, but learned HTP words better than HTP violations. Thus, by 2 years of age sensitivity to TPs does not lead to an HTP advantage but rather to poor mapping of violations of HTP word forms. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Can Infants Retain Statistically Segmented Words and Mappings Across a Delay?

Infants are sensitive to statistics in spoken language that aid word-form segmentation and immediate mapping to referents. However, it is not clear whether this sensitivity influences the formation and retention of word-referent mappings across a delay, two real-world challenges that learners must overcome. We tested how the timing of referent training, relative to familiarization with transitional probabilities (TPs) in speech, impacts English-learning 23-month-olds' ability to form and retain word-referent mappings. In Experiment 1, we tested infants' ability to retain TP information across a 10-min delay and use it in the service of word learning. Infants successfully mapped high-TP but not low-TP words to referents. In Experiment 2, infants readily mapped the same words even when they were unfamiliar. In Experiment 3, high- and low-TP word-referent mappings were trained immediately after familiarization, and infants readily remembered these associations 10 min later. In sum, although 23-month-old infants do not need strong statistics to map word forms to referents immediately, or to remember those mappings across a delay, infants are nevertheless sensitive to these statistics in the speech stream, and they influence mapping after a delay. These findings suggest that, by 23 months of age, sensitivity to statistics in speech may impact infants' language development by leading word forms with low coherence to be poorly mapped following even a short period of consolidation.

Validation of an open source, remote web-based eye-tracking method (WebGazer) for research in early childhood

Measuring eye movements remotely via the participant's webcam promises to be an attractive methodological addition to in-person eye-tracking in the lab. However, there is a lack of systematic research comparing remote web-based eye-tracking with in-lab eye-tracking in young children. We report a multi-lab study that compared these two measures in an anticipatory looking task with toddlers using WebGazer.js and jsPsych. Results of our remotely tested sample of 18-27-month-old toddlers (N = 125) revealed that web-based eye-tracking successfully captured goal-based action predictions, although the proportion of the goal-directed anticipatory looking was lower compared to the in-lab sample (N = 70). As expected, attrition rate was substantially higher in the web-based (42%) than the in-lab sample (10%). Excluding trials based on visual inspection of the match of time-locked gaze coordinates and the participant's webcam video overlayed on the stimuli was an important preprocessing step to reduce noise in the data. We discuss the use of this remote web-based method in comparison with other current methodological innovations. Our study demonstrates that remote web-based eye-tracking can be a useful tool for testing toddlers, facilitating recruitment of larger and more diverse samples; a caveat to consider is the larger drop-out rate.

Speech Segmentation and Cross-Situational Word Learning in Parallel

Language learners track conditional probabilities to find words in continuous speech and to map words and objects across ambiguous contexts. It remains unclear, however, whether learners can leverage the structure of the linguistic input to do both tasks at the same time. To explore this question, we combined speech segmentation and cross-situational word learning into a single task. In Experiment 1, when adults (N = 60) simultaneously segmented continuous speech and mapped the newly segmented words to objects, they demonstrated better performance than when either task was performed alone. However, when the speech stream had conflicting statistics, participants were able to correctly map words to objects, but were at chance level on speech segmentation. In Experiment 2, we used a more sensitive speech segmentation measure to find that adults (N = 35), exposed to the same conflicting speech stream, correctly identified non-words as such, but were still unable to discriminate between words and part-words. Again, mapping was above chance. Our study suggests that learners can track multiple sources of statistical information to find and map words to objects in noisy environments. It also prompts questions on how to effectively measure the knowledge arising from these learning experiences.

Combining statistics: the role of phonotactics on cross-situational word learning

Language learners can rely on phonological and semantic information to learn novel words. Using a cross-situational word learning paradigm, we explored the role of phonotactic probabilities on word learning in ambiguous contexts. Brazilian-Portuguese speaking adults (N = 30) were exposed to two sets of word-object pairs. Words from one set of labels had slightly higher phonotactic probabilities than words from the other set. By tracking co-occurrences of words and objects, participants were able to learn word-object mappings similarly across both sets. Our findings contrast with studies showing a facilitative effect of phonotactic probability on word learning in non-ambiguous contexts.

The development of gaze following in monolingual and bilingual infants: A multi-laboratory study

Determining the meanings of words requires language learners to attend to what other people say. However, it behooves a young language learner to simultaneously encode relevant non-verbal cues, for example, by following the direction of their eye gaze. Sensitivity to cues such as eye gaze might be particularly important for bilingual infants, as they encounter less consistency between words and objects than monolingual infants, and do not always have access to the same word-learning heuristics (e.g., mutual exclusivity). In a preregistered study, we tested the hypothesis that bilingual experience would lead to a more pronounced ability to follow another's gaze. We used a gaze-following paradigm developed by Senju and Csibra (Current Biology, 18, 2008, 668) to test a total of 93 6- to 9-month-old and 229 12- to 15-month-old monolingual and bilingual infants, in 11 laboratories located in 8 countries. Monolingual and bilingual infants showed similar gaze-following abilities, and both groups showed age-related improvements in speed, accuracy, frequency, and duration of fixations to congruent objects. Unexpectedly, bilinguals tended to make more frequent fixations to on-screen objects, whether or not they were cued by the actor. These results suggest that gaze sensitivity is a fundamental aspect of development that is robust to variation in language exposure.

Mapping non-native pitch contours to meaning: Perceptual and experiential factors

Infants show interesting patterns of flexibility and constraint early in word learning. Here, we explore perceptual and experiential factors that drive associative learning of labels that differ in pitch contour. Contrary to the salience hypothesis proposed in Experiment 1, English-learning 14-month-olds failed to map acoustically distinctive level and dipping labels to novel referents, even though they discriminated the labels when no potential referents were present. Conversely, infants readily mapped the less distinctive rising and dipping labels. In Experiment 2, we found that the degree of pitch variation in labels also does not account for learning. Instead, English-learning infants only learned if one of the labels had a rising pitch contour. We argue that experience with hearing and/or producing native language prosody may lead infants to initially over-interpret the role rising pitch plays in differentiating words. Together, our findings suggest that multiple factors contribute to whether specific acoustic forms will function as candidate object labels.

Intersecting Constraints on Label Learning: Effects of Age, Label Properties, and Referential Context

This research investigates the development of constraints in word learning. Previous experiments have shown that as infants gain more knowledge of native language structure, they become more selective about the forms that they accept as labels. However, the developmental pattern exhibited depends greatly on the way that infants are introduced to the labels and tested. In a series of experiments, we examined how providing referential context in the form of familiar objects and familiar object names affects how infants learn labels that they would otherwise reject, nonspeech sounds. We found evidence of the development of intersecting constraints: Younger infants (14-month-olds) were more open to learning nonspeech tone labels than older infants (19-month-olds), and younger infants were more open to the influence of referential context. These findings suggest that infants form expectations about labels and labeling contexts as they become more sophisticated learners.

Do Infants Learn Words From Statistics? Evidence From English-Learning Infants Hearing Italian

Infants are sensitive to statistical regularities (i.e., transitional probabilities, or TPs) relevant to segmenting words in fluent speech. However, there is debate about whether tracking TPs results in representations of possible words. Infants show preferential learning of sequences with high TPs (HTPs) as object labels relative to those with low TPs (LTPs). Such findings could mean that only the HTP sequences have a word-like status, and they are more readily mapped to a referent for that reason. But these findings could also suggest that HTP sequences are easier to encode, just like any other predictable sequence. Here we aimed to distinguish between these explanations. To do so, we built on findings that infants become resistant to learning labels that are not typical of their native language as they approach 2 years of age and add words to their lexicons. If tracking TPs in speech results in identifying candidate words, at this age TPs may have reduced power to confer lexical status when they yield a unit that is very dissimilar to word forms that are typical of infants' native language. Indeed, we found that at 20 months, English-learning infants with relatively small vocabularies learned HTP Italian words (but not LTP words) as object labels, while infants with larger vocabularies resisted learning HTP Italian words. These findings suggest that the HTP sequences may be represented as candidate words, and more broadly, that TP statistics are relevant to word learning.

The longevity of statistical learning: When infant memory decays, isolated words come to the rescue

Research over the past 2 decades has demonstrated that infants are equipped with remarkable computational abilities that allow them to find words in continuous speech. Infants can encode information about the transitional probability (TP) between syllables to segment words from artificial and natural languages. As previous research has tested infants immediately after familiarization, infants' ability to retain sequential statistics beyond the immediate familiarization context remains unknown. Here, we examine infants' memory for statistically defined words 10 min after familiarization with an Italian corpus. Eight-month-old English-learning infants were familiarized with Italian sentences that contained 4 embedded target words-2 words had high internal TP (HTP, TP = 1.0) and 2 had low TP (LTP, TP = .33)-and were tested on their ability to discriminate HTP from LTP words using the Headturn Preference Procedure. When tested after a 10-min delay, infants failed to discriminate HTP from LTP words, suggesting that memory for statistical information likely decays over even short delays (Experiment 1). Experiments 2-4 were designed to test whether experience with isolated words selectively reinforces memory for statistically defined (i.e., HTP) words. When 8-month-olds were given additional experience with isolated tokens of both HTP and LTP words immediately after familiarization, they looked significantly longer on HTP than LTP test trials 10 min later. Although initial representations of statistically defined words may be fragile, our results suggest that experience with isolated words may reinforce the output of statistical learning by helping infants create more robust memories for words with strong versus weak co-occurrence statistics. (PsycINFO Database Record

From flexibility to constraint: the contrastive use of lexical tone in early word learning

Infants must develop both flexibility and constraint in their interpretation of acceptable word forms. The current experiments examined the development of infants' lexical interpretation of non-native variations in pitch contour. Fourteen-, 17-, and 19-month-olds (Experiments 1 and 2, N = 72) heard labels for two novel objects; labels contained the same syllable produced with distinct pitch contours (Mandarin lexical tones). The youngest infants learned the label-object mappings, but the older groups did not, despite being able to discriminate pitch differences in an object-free task (Experiment 3, N = 14). Results indicate that 14-month-olds remain flexible regarding what sounds make meaningful distinctions between words. By 17-19 months, experience with a nontonal native language constrains infants' interpretation of lexical tone.

Rhythmic grouping biases constrain infant statistical learning

Linguistic stress and sequential statistical cues to word boundaries interact during speech segmentation in infancy. However, little is known about how the different acoustic components of stress constrain statistical learning. The current studies were designed to investigate whether intensity and duration each function independently as cues to initial prominence (trochaic-based hypothesis) or whether, as predicted by the Iambic-Trochaic Law (ITL), intensity and duration have characteristic and separable effects on rhythmic grouping (ITL-based hypothesis) in a statistical learning task. Infants were familiarized with an artificial language (Experiments 1 & 3) or a tone stream (Experiment 2) in which there was an alternation in either intensity or duration. In addition to potential acoustic cues, the familiarization sequences also contained statistical cues to word boundaries. In speech (Experiment 1) and non-speech (Experiment 2) conditions, 9-month-old infants demonstrated discrimination patterns consistent with an ITL-based hypothesis: intensity signaled initial prominence and duration signaled final prominence. The results of Experiment 3, in which 6.5-month-old infants were familiarized with the speech streams from Experiment 1, suggest that there is a developmental change in infants' willingness to treat increased duration as a cue to word offsets in fluent speech. Infants' perceptual systems interact with linguistic experience to constrain how infants learn from their auditory environment.

Linking sounds to meanings: infant statistical learning in a natural language

The processes of infant word segmentation and infant word learning have largely been studied separately. However, the ease with which potential word forms are segmented from fluent speech seems likely to influence subsequent mappings between words and their referents. To explore this process, we tested the link between the statistical coherence of sequences presented in fluent speech and infants' subsequent use of those sequences as labels for novel objects. Notably, the materials were drawn from a natural language unfamiliar to the infants (Italian). The results of three experiments suggest that there is a close relationship between the statistics of the speech stream and subsequent mapping of labels to referents. Mapping was facilitated when the labels contained high transitional probabilities in the forward and/or backward direction (Experiment 1). When no transitional probability information was available (Experiment 2), or when the internal transitional probabilities of the labels were low in both directions (Experiment 3), infants failed to link the labels to their referents. Word learning appears to be strongly influenced by infants' prior experience with the distribution of sounds that make up words in natural languages.

Learning in reverse: eight-month-old infants track backward transitional probabilities

Numerous recent studies suggest that human learners, including both infants and adults, readily track sequential statistics computed between adjacent elements. One such statistic, transitional probability, is typically calculated as the likelihood that one element predicts another. However, little is known about whether listeners are sensitive to the directionality of this computation. To address this issue, we tested 8-month-old infants in a word segmentation task, using fluent speech drawn from an unfamiliar natural language. Critically, test items were distinguished solely by their backward transitional probabilities. The results provide the first evidence that infants track backward statistics in fluent speech.

Statistical learning in a natural language by 8-month-old infants

Numerous studies over the past decade support the claim that infants are equipped with powerful statistical language learning mechanisms. The primary evidence for statistical language learning in word segmentation comes from studies using artificial languages, continuous streams of synthesized syllables that are highly simplified relative to real speech. To what extent can these conclusions be scaled up to natural language learning? In the current experiments, English-learning 8-month-old infants' ability to track transitional probabilities in fluent infant-directed Italian speech was tested (N = 72). The results suggest that infants are sensitive to transitional probability cues in unfamiliar natural language stimuli, and support the claim that statistical learning is sufficiently robust to support aspects of real-world language acquisition.

Enhanced contrast for vowels in utterance focus: a cross-language study

The present study examined several potential distinctiveness-enhancing correlates of vowels produced in utterance focus by talkers of American English, French, and German. These correlates included possible increases in vowel space size, in formant movement within individual vowels, and in duration variance among vowels. Each language group enhanced the distinctiveness of vowels in [+focus] context but used somewhat differing means to achieve this. All three groups used spectral differences, but only German talkers used durational differences, to enhance distinctiveness. The results suggest that the amount of distinctiveness enhancement of a vowel property in [+focus] context is positively related to the between-category variation of that property in [-focus] context. Thus, consistent with the theory of adaptive dispersion, utterance clarity appears to vary directly with information content.

An investigation of speech perception in children with specific language impairment on a continuum of formant transition duration

Fifteen children diagnosed with specific language impairment (SLI) and 15 typically developing (TD) children were tested for identification performance on 2 synthetic speech continua varying in formant transition durations (FTDs). One continuum varied from /ba/ to /wa/, and the other varied from /da/ to /ja/. Various d'-related measures from signal detection theory were used to compare category boundaries and indirectly derive sensitivity to phonetic changes in category tokens along each continuum. The SLI group showed less consistent identification performance along the /ba/-/wa/ series relative to the TD group, as well as reduced sensitivity to phonetic changes along the continuum. On the /da/-/ja/ series, the SLI group revealed less consistent identification performance on the short FTD end but similar identification levels to the TD group at the long FTD end. The overall results support the contention that children with SLI reveal a deficiency in the processing of speech sounds at the level of segmental identity.

Proactive interference, accessibility bias, and process dissociations: valid subjective reports of memory

Proactive interference was assessed with a variant of the process-dissociation procedure, which separates effects of habit (accessibility bias) and recollection (discriminability). In three cued-recall experiments, proactive interference was shown to be an effect of bias rather than an effect on actual remembering. Divided attention, age, and study duration selectively influenced the recollection parameter, whereas training probability selectively influenced the habit parameter. Furthermore, in Experiments 2 and 3, subjective reports of remembering were highly correlated with, and nearly identical to, objective estimates of recollection gained from the process-dissociation procedure. The authors discuss the relevance of the results to theories of proactive interference and argue that older adults' greater susceptibility to interference effects is sometimes caused by an inability to recollect rather than by an inability to inhibit a preponderant response.

Separating habit and recollection in young and older adults: effects of elaborative processing and distinctiveness

An extension of L. L. Jacoby's (1991) process-dissociation procedure was used to examine the effects of aging on recollection and automatic influences of memory (habit). Experiment 1 showed that older adults were impaired in their ability to engage in recollection but did not differ from young adults in their reliance on habit. Elderly adults were also less able to exploit distinctive contextual information to enhance recollection. Experiments 2 and 3 showed that with more supportive conditions, older adults were able to benefit from distinctive contextual information. Quantitative and qualitative deficits in recollective abilities are interpreted within a dual-process model of memory. The problem of distinguishing between a deficit in recollection and a deficit in inhibitory processes in older adults (e.g., L. Hasher & R. T. Zacks, 1988) and the importance of this distinction for purposes of repairing memory performance are discussed.

Aging and judgments of duration: effects of task complexity and method of estimation

The effects of aging on judgments of short temporal durations were explored using the prospective paradigm and the methods of verbal estimation and production. Younger and older adults performed a perceptual judgment task at five levels of complexity for periods of 30, 60, and 120 sec. Participants either continued to perform the task for a specified interval (production) or were stopped and then verbally estimated the interval. Older adults gave shorter verbal estimates and longer productions than did younger adults. The methods of verbal estimation and production yielded approximately equal duration judgment ratios once range effects were taken into account. Task complexity had little effect. The major conclusion is that duration judgment ratios decrease from younger to older adults when the intervals are filled with a mental task.

Separating habit and recollection in young and older adults: effects of elaborative processing and distinctiveness

An extension of L. L. Jacoby's (1991) process-dissociation procedure was used to examine the effects of aging on recollection and automatic influences of memory (habit). Experiment 1 showed that older adults were impaired in their ability to engage in recollection but did not differ from young adults in their reliance on habit. Elderly adults were also less able to exploit distinctive contextual information to enhance recollection. Experiments 2 and 3 showed that with more supportive conditions, older adults were able to benefit from distinctive contextual information. Quantitative and qualitative deficits in recollective abilities are interpreted within a dual-process model of memory. The problem of distinguishing between a deficit in recollection and a deficit in inhibitory processes in older adults (e.g., L. Hasher & R. T. Zacks, 1988) and the importance of this distinction for purposes of repairing memory performance are discussed.

Separating habit and recollection: memory slips, process dissociations, and probability matching

Memory slips are errors in performance that result when an automatic basis for responding (e.g., habit) opposes the intention to perform a specific behavior. Prior research has focused on factors that influence the probability of a memory slip while neglecting factors that facilitate performance. Using L. L. Jacoby's (1991) process-dissociation procedure to examine performance in both a memory-slip and a facilitation condition, the authors separated the contribution of habit and recollection (intentional memory) in a cued-recall task. The authors found that manipulating the strength of habit affected its contribution to performance in a manner that produced probability matching, but recollection was unchanged. In contrast, manipulations of presentation rate and response time influenced recollection but did not affect habit. Such dissociations support a model of memory in which automatic and intentional influences make independent contributions to performance.

Separating habit and recollection: memory slips, process dissociations, and probability matching

Memory slips are errors in performance that result when an automatic basis for responding (e.g., habit) opposes the intention to perform a specific behavior. Prior research has focused on factors that influence the probability of a memory slip while neglecting factors that facilitate performance. Using L. L. Jacoby's (1991) process-dissociation procedure to examine performance in both a memory-slip and a facilitation condition, the authors separated the contribution of habit and recollection (intentional memory) in a cued-recall task. The authors found that manipulating the strength of habit affected its contribution to performance in a manner that produced probability matching, but recollection was unchanged. In contrast, manipulations of presentation rate and response time influenced recollection but did not affect habit. Such dissociations support a model of memory in which automatic and intentional influences make independent contributions to performance.